The present invention relates to devices for the fixation and/or support of bones. In particular, the present invention relates to a spinal plate assembly, and a corresponding spinal plate, for the fixation and/or support of bones of the spinal column. The plate of the present invention has particular application in situations where compressional or settling forces, as well as torsional and flexing forces, of “fixed” vertebrae on a spinal plate cause significant stressing and potential failure of the spinal plate and/or plate components.
Vertebral fixation has become a common approach to treating spinal disorders and fractures, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more vertebrae are fixed in position relative to one or more other vertebrae above and/or below the vertebrae to be fixed. Generally, a spinal plate is the device of choice used for mechanically supporting such vertebral fixation. A typical spinal plate includes a plate having a plurality of apertures therethrough. A plurality of fasteners, i.e., bone screws, are generally positioned into and through respective ones of the apertures of the plate to thereby attach the spinal plate to bone, such as to two or more respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to thereby attach the spinal plate to the respective vertebrae. In general, such plate and screw assemblies can be utilized, for example, for anterior fixation of the spine for cervical, lumbar, and/or thoracic fixation.
The basis of anterior fixation or plating is to approach the spine from an anterior or anterio-lateral approach, and use the screws to solidly mount the spinal plate to the affected vertebrae. In addition to the application of a spinal plate, graft material may be combined in an attempt to permanently fuse together adjacent vertebrae. The graft material can consist of bone grafts obtained from bones of the recipient or another individual.
A common problem associated with the use of such spinal plates is the tendency of the bone screws to “back out” or pull away or otherwise withdraw from the bone into which they are mounted. This problem occurs primarily due to the normal torsional and bending motions of the body and spine. This is a particularly important problem because as the screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the spinal plate and, possibly, even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient user of the spinal plate, this condition can also create a number of potentially serious physiological problems given the significant amount of nervous and vascular structures located at or near the potential locations of anterior spinal plate fixations.
A number of plate assembly designs have been proposed in attempts to prevent screws from pulling away or withdrawing from the bone and/or to prevent the screws from backing out or pulling away or withdrawing from the surface of the spinal plate. Such mechanisms used to prevent bone screws from pulling out of bones include cams which engage and lock the screws, and the use of expanding head screws which expand outwardly when adequate force is applied thereto to engage the holes in the spinal plate. All of these designs have detriments, which include potential for breakage of the screws, or which require particular precision and alignment in their application in order to work correctly. Additionally, loose components and accessories of spinal plates, which address the “backing-out” or withdrawal problem, can get dropped and/or misplaced while the vertebral fixation surgical procedure is taking place, prolonging and complicating the procedure as well as creating substantial risk of harm to the recipient.
Yet another common problem associated with the use of such spinal plates is the tendency, of the vertebrae which are being treated to settle after the spinal plate has been installed. Such settling adds compression forces to the above-listed forces, and raises the probability that the bone screws will break, will back out, or pull away, or otherwise withdraw, from the bone to which they were mounted.
It is an object of the invention to provide spinal plate assemblies which facilitate secure bone-to-bone fixation and/or support, such as at e.g. adjacent or second adjacent vertebrae, while accommodating post-procedural compression between the respective bones.
It is another object of the invention to provide spinal plate assemblies which afford substantial protection against pulling away or withdrawal of mounting components, which pulling away or withdrawal may result from e.g. torsional movement, flexing movement, or stress and/or dynamic load sharing of the vertebrae, the protection thereby enhancing the bone rebuilding process carried on routinely by the living body.
It is yet another object of the invention to provide spinal plate assemblies which attenuate application of stress on the plate apparatus and on the affixing components.
It is a further object of the invention to provide spinal plate assemblies comprising a spinal plate and resiliently movable spring-like material having resilient properties, the assemblies being so mounted and positioned as to enable bone fasteners to move past such spring-like material, with corresponding flexing or other movement of such spring-like material, when the bone fasteners are being installed in a recipient user and which, in combination with the designs of the bone fasteners, prevent unintentional withdrawal of the bone fasteners after installation of the bone fasteners in the recipient user.
It is yet a further object of the invention to provide spinal plate assemblies which can be completely pre-assembled such that no assembly steps need be performed on the spinal plate assembly, itself, while the spinal plate assembly is being installed in a recipient user thereof.
It is still a further object of the invention to provide spinal plate assemblies wherein apparatus, in such spinal plate assemblies, for preventing withdrawal of bone fasteners from the bone, after installation of the bone fasteners in a recipient user, are automatically activated, to prevent such withdrawal, as a consequence of the installation of suitably-configured such bone fasteners.